homework encyclopedia

192 Science and Technology

Telecommunications are messages carried round the

world in seconds by electric signals and waves from the

. ELECTROMAGNETIC SPECTRUM. They include radio

and television broadcasts, and telephone conversations.

HOW DOES A MOBILE PHONE WORK?

A mobile (or cell) phone sends and receives signals

using microwaves. A phone has a range of only a few

miles, so land-based aerials are used. The area that

each aerial covers is called a cell. A phone exchanges

signals with the nearest aerial. As you move from cell

to cell the phone changes aerials. The aerials are

connected to the global telephone network.

HOW DOES A TELEPHONE WORK?

A telephone has a microphone and an earpiece. The

microphone converts sound into an electric signal.

The signal travels at the speed of light along wires,

through optical fibres, or via microwaves. A network

connects the phones. The earpiece contains a

loudspeaker. This changes the signal back into sound.

HOW DOES A RADIO WORK?

Radio broadcasts are made from a central transmitter.

Sound signals from microphones in the radio studio

are combined with radio waves broadcast from an

antenna. Your radio at home has a receiver that

separates the sound signal from the radio signal and

sends it to a loudspeaker. This is the sound you hear.

HOW DOES A TELEVISION WORK?

An analogue television transmitter sends pictures and

sounds as a pattern of radio waves through cables.

. DIGITAL BROADCASTS transmit the sounds and
pictures in binary code through cables and satellites.

TELEPHONE TOWER 3

The BT tower in London,

England, provides

telecommunications links into

and out of the city. It is an

electronic communications

centre for radio and television

broadcasting, telephone

services, and digital computer

data transmissions.

4 COMMUNICATIONS SATELLITE

A satellite bounces

telecommunications signals

from one side of Earth to

another. The satellite travels

in a geostationary orbit so that

it stays over the same point on

Earth’s surface at all times.

Telecommunications

4 HIDDEN MOBILE PHONE MAST

To create an effective mobile

phone network, mobile phone

masts are built at regular

intervals nationwide. In some

locations, masts spoil attractive

views of the countryside or

historic buildings. This mast has

been disguised as a tree.

Dish-shaped

microwave

antennae point

towards similar

dishes on masts

in other cities

Aircraft warning

beacons flash

on the top and

sides of the

tower at night

GUGLIELMO MARCONI

Italian, 1874-1937

Scientist and inventor

Guglielmo Marconi made the

first radio transmissions in

1894. His transmitter rang a
      bell 10 m (30 ft) away. By
      1901, he had developed his
      invention and made the first
      wireless transmission across
      the Atlantic Ocean from
      England to Canada. Marconi
      was awarded the Nobel Prize
      for Physics in 1909.

telecoms